PCBC-217: Add package.xml to build with PECL

Change-Id: Iad0155c29285851c1e1badfa6e3e6d3f8f33f2f1
Reviewed-on: http://review.couchbase.org/25445
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>